Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $71.40   3.598%   $73.969   $73.97   $73.95   $74.00  
  Purchase #2 $114.47   6.503%   $121.914   $121.91   $121.90   $121.90  
  Purchase #3 $101.37   8.363%   $109.8476   $109.85   $109.85   $109.80  
  Purchase #4 $220.39   3.325%   $227.718   $227.72   $227.70   $227.70  
  Purchase #5 $95.43   9.402%   $104.4023   $104.40   $104.40   $104.40  
  Purchase #6 $111.29   3.298%   $114.9603   $114.96   $114.95   $115.00  
  Purchase #7 $88.62   5.192%   $93.2212   $93.22   $93.20   $93.20  
  7 purchase totals = $802.97       $846.0324   $846.03   $845.95   $846.00